Kingpin assemblies, used in heavy motor vehicles such as trucks and the like, consist generally of a circularly cylindrical kingpin extending through a substantially vertical bore in a vehicle front axle, and through integral upper and lower yokes of a steering spindle knuckle which straddle the axle end. The central portion of the kingpin is fixedly secured within the bore of the front axle, with the upper and lower ends of the kingpin residing within respective upper and lower yokes of the steering spindle knuckle. The steering spindle knuckle is pivotable relative to the kingpin and oscillates about the upper and lower kingpin ends which project above and below the axle.
In heavy duty truck applications, the bearing load on the kingpin is often 12,000 or 13,000 lbs. minimum. To take such loads, the kingpins are journaled in brass bronze bushings that are typically 13/4 inches in height and 11/2 inches diameter, and nominally should last for 100,000 miles. If not greased properly, these bushings usually last 80,000 miles or less or they may, when greased properly, last as much as 150,000 miles. Some kingpin assemblies use a thicker brass bushing of 2.00 inches diameter which nominally should last 300,000 miles; but when not properly greased, they usually last about 200,000 to 225,000 miles. One reason that the kingpin assemblies for heavy duty applications are not greased timely and properly is that the wheel on the spindle of the kingpin assembly must be jacked off the ground to relieve the pressure of the kingpin against the bushing to allow grease to flow entirely about the kingpin and the bushing. The jacking of the wheels is a time-consuming and costly process that is also dangerous; and consequently, truckers are reluctant to do it. Furthermore, there is a problem of a gasket being blown out during a greasing operation, particularly when the temperature is very cold. The kingpin assembly has a cap with a grease fitting over the gasket; and in cold temperature, the grease may be pumped at such high pressures through a grease fitting on the cap that the gasket is blown out.
The kingpins in heavy duty applications are heavy and expensive, e.g., 50 lbs. in weight and a cost of $700 may be typical. Often in these conventional kingpin assemblies, the spindle becomes worn and then the spindle is removed and honed down in diameter at its ends; and then a thicker bushing must be used with the smaller diameter, honed spindle end. If the bushing becomes too worn, the kingpin will gouge the bore wall in the yoke of the steering spindle knuckle. It is a very expensive operation to remove and to replace a damaged kingpin, and to rebore the steering spindle knuckle.
Furthermore, these traditional kingpin assemblies with brass bronze bushings are not designed to provide long term lubrication because the load on the kingpin causes the kingpin to bear at a point or line of contact with the bushing wall with sufficient pressure to squeeze the grease away from the point or line of contact. Without lubrication precisely where it is most needed at the point of contact, the kingpin and bushing wear more quickly and may ultimately fail.
Some trucks sold by Volvo White Truck Corporation used needle bearings rather than brass bushings to journal the kingpins for turning movement. However, it is recommended that for a lubrication of these needle bearings, that the front axle be lifted so that there is no load on the wheels. Also, because the needle bearings are force-fitted into the bore in the yokes of steering knuckles, they are difficult to replace.
It is not uncommon to replace conventional bushings or bearings several times during the useful life of a heavyweight vehicle. Hence, improved life for the kingpin bearings and an easier manner of removal of these bushings or bearings, than the usual removal of high pressure tools to remove them from their press fit tightly in the yokes are highly desirable. Additionally, there is a need for an improved kingpin assembly and its bearings that are not prohibitively costly and can be used with conventional yokes of existing trucks for use in the retrofit market as well as for use in the original equipment market.
In some instances for lighter duty applications, tapered, plastic bushings and tapered ends on the kingpin have been proposed, such as in U.S. Pat. No. 3,477,771. However, plastic bushings cannot withstand the 12,000 lb. or greater loads that are used in heavy trucks and will fail; and the tapered ends of the kingpins will lift up the tapered bushings at 12,000 lbs. of force. Hence, such a construction is not practical for use in heavy duty trucks.
Traditionally, it was not uncommon for a kingpin assembly to require a greasing every 5,000 miles. Single seal arrangements, common in such assemblies, not only allow moisture to escape from the assembly, but they allow moisture to get in as well. The presence of moisture not only decreases the tolerance between the seal and the shaft, but in increased wear in the kingpin assembly in general, among other negative affects.
Over time, with the development of new types of seal materials, the period between greasings was increased to 25,000 miles, then to 50,000 miles, and now to as much as 100,000 miles. Even with this improvement, the maintenance operation of kingpin greasing--requiring the expenditure of time and money--remained. Hence, it would be beneficial to develop an improved seal that will eliminate the need for this greasing operation.